Alloy for addition to iron or steel



United States Patent ALLOY FOR ADDITION TO IRON OR STEEL Daniel LeonardEdlund, Bethel, Pa., assignor to Vanadium Corporation of America, NewYork, N. Y., a corporation of Delaware No Drawing. Application August20, 1952, Serial No. 305,509

4 Claims. (Cl. 75167) This invention relates to a uniform, homogeneousalloy for the control and improvement of the physical properties of castiron and for other uses, such as the treatment of steel in the moltenstate.

This application is a continuation-in-part of my copending applicationSerial No. 183,663 filed September 7, 1950, now abandoned.

Cast iron is a generic term which includes gray irons, white cast irons,chilled cast irons and malleable irons. The properties of these metalsdepend in part upon chemical factors (principally the percentages ofcarbon and silicon) and in part upon physical factors, both asinfluenced by conditions related to the manufacturing methods. This isso because cast iron is essentially the product of a process and theinfluence of the process details are observed in the qualities of theprod uct. Alloying is employed to alter the properties of some castirons; also some iron castings both alloyed and not alloyed aresubjected to thermal treatments to produce desired results in castingsfor specific uses. The physical structure (i. e. the nature anddistribution of the micro-constituents), and consequently the propertiesof the metal are influenced not only by these several factors but alsoby adjusting the maximum temperature attained by the molten iron and thecooling rate both during and after solidification.

Cast iron is sometimes considered unsatisfactory as a material ofconstruction because of its low strength and lack of ductility whencompared to steel and certain other engineering alloys. In such acomparison cast iron is usually described as being inherently brittle,especially in the as-cast condition; this brittleness can be reducedonly to a very limited extent by heat-treatment, except for long andcostly treatments applied to irons in the malleable iron compositionrange.

The cast iron which is most used commercially for constructionalapplications, however, is gray iron, but this term actually covers awide range of compositions with corresponding widely varying properties.The composition of gray iron is usually confined within the limits 0.50to 2.75% silicon and 2.70 to 3.60% total carbon. Within this range ofcomposition the tensile strength may vary from 15,000 to 60,000 poundsper square inch and occasionally higher.

While a part of the carbon present in gray cast iron may be in thecombined form as iron carbide, the greater amount is present inelemental form as graphite. The relative amounts of free carbon andcombined carbon, as well as the shape, size and distribution of theparticles are dependent upon the remaining chemical composition of theiron and the influences referred to above, namely, maximum temperaturein the liquid state, rate of cooling during and after solidification,and types of heat treatment, if any, applied to a solidified casting.

Elements incidental to the production of cast iron may add or detractfrom its properties, such as strength, toughness and ductility. Sulphur,for example, is usually kept as low as possible because while itincreases the strength of the iron to some degree, it very markedlyreduces ductility. Control of sulphur depends, however, on raw materialsand process and often it cannot be held to very low values because onlyhigh-sulphur raw materials are available, the cost of electric furnacerefining may not be permissible and chemical treatment may not beadequate or sufficiently uniform. Phosphorous occasionally strengthensiron but in large amounts renders it quite brittle.

2,706,681 Patented Apr. 19, 1955 Certain elements usually considered asalloying agents have been added to control the structure and propertiesof cast iron. In some cases the addition of such alloys results in oneproperty being improved to the detriment of another; for example,strength may be improved but the toughness of the iron be reduced unlesssome adequate form of heat-treatment is provided to retain thetoughness. In other cases improvement in strength is accompanied byreduction in the machinability of the iron; in some of these casesheat-treatment, such as annealing, may restore the machinability.

It is known that magnesium added to iron which would otherwise cast grayor nearly so contributes to this iron high strength and some ductility.The ductility has in some cases been found to be increased by anannealing treatment with relatively little sacrifice in this superiorstrength.

However, serious difficulties have beset attempts to make this magnesiumpractice one that would provide with assurance successive reproductionin continuous manufacturing operations of iron articles of high strengthor high strength and good ductility. The boiling point of magnesiumbeing considerably below both the melting temperatures of those metalswith which it is preferably combined for making addition agents andbelow the temperatures at which cast iron is tapped and poured, causesextreme difficulty in controlling the overall recovery of magnesium fromraw material to the finished cast iron product.

The boiling point of magnesium is about 2030 R, which results in veryhigh losses due to vaporization of the magnesium when it is added tomolten copper and molten nickel to produce such addition agents as 20%magnesium and 80% copper, and 20% magnesium and 80% nickel. Furtherdifiiculty is presented when it is attempted to introduce iron intothese compositions. Iron is a very desirable carrier metal whenmagnesium is to be introduced into iron alloys, such as gray cast ironor steel. The introduction of iron into the copper or nickel base alloysmentioned above, however, only increases the already high losses ofmagnesium during manufacture.

Since the temperature of cast iron flowing from the cupola is normallyin the range 2300 to 2800 F., it is obvious that additional losses willbe encountered through vaporization when magnesium alloys are added toiron. When pure metallic magnesium is added to cast iron at such pouringtemperatures, its volatilization can be explosive in character.Magnesium continues to vaporize as long as the iron remains molten andthe time element combined with the initial violent reaction results invariable losses and properties that vary beyond the limits ofsatisfactory commercial control. The use of alloy addition agents, suchas the 20% magnesium and 80% copper, and 20% magnesium and 80% nickelcompositions previously mentioned, does not satisfactorily overcomethese difliculties. For example, if the cast iron to which such alloysare added is on the high side of the above temperature range, a violentreaction will occur with high losses of magnesium through volatilizationas well as loss of metal and danger to the operators through spatteringof the molten cast iron. If, on the other hand, the temperature of theiron is low, incomplete solution may occur, resulting in segregation andin variation in both structure and properties throughout the product.

I have discovered in the course of extended experiments directed towardthe development of a commercially satisfactory practice for producingmagnesiumcontaining cast iron of predictable and reproducibleproperties, that by a process involving the manufacture and use ofcertain uniform, homogeneous alloys of magnesium, silicon and lead, anunexpected solution to these problems is presented. The alloys may alsocontain iron or manganese or both iron and manganese. Primarily, myinvention consists in a process whereby magnesium may be converted to aform satisfactory for the treatment of cast iron with greater overallrecovery of magnesium from the raw materials to the finished ironcasting.

More particularly, my discovery consists in a certain criticalcombination in the proportions of magnesium,

silicon and lead in a uniform, homogeneous alloy, which alloy maycontain iron or manganese or both, the proportions of the ingredientsbeing such as to substantially increase the recovery of magnesium in themanufacture of the addition agent as well as when this agent is added tomolten cast iron. This combination of effects provides a significantcost saving. More significant, however, is the fact that when usingalloys within the limits of my invention, the desired improvements inthe finished cast iron are obtainable more readily and with much greaterregularity. \Vhile cast iron in which substantially all of the carbon isin the form of spheroids has been produced frequently, it has beendifiicult to obtain structurally perfect castings under productionconditions with a variety of designs, melting equipment, raw materialsand other foundry conditions. A much closer approach to perfection canbe attained in the use of alloys herein described.

The alloys which have produced the advantages described are uniform andhomogeneous and contain about 5 to 30% magnesium, about to 40% silicon,and about to 70% lead. Contrary to the experience of prior practice, ithas been found that in the presence of this amount of lead in thesecomplex alloys, the maximum magnesium content may be somewhat higherthan customarily employed without danger of severe spattering orexplosive violence; presumably the vapor pressure of magnesium isbeneficially affected by association with the lead. Iron or manganese orboth may also be present in these alloys. Similarly, while contrary toexpectations, based upon their relative ease of combination with oxygen,nitrogen, etc., the silicon, and the manganese when present, in thesealloys, have the effect of restraining the loss of magnesium on additionto molten iron, thereby reducing the amount of magnesium that need beadded to effect a given magnesium recovery in the solidified iron. Ironor manganese or both in the presence of the minimum percentage of leadabove noted, appear to behave similarly to the lead in restraining theviolence of the reaction. The limits, however, upon iron and manganeseappear to be critical. The manganese should not exceed about 12% in viewof the fact that for the magnesium addition customarily practiced theamount of manganese introduced would tend too greatly toward stabilizingpearlite in the cast iron matrix and render it difiicult to secure themaximum ductility that results from maximum ferrite in the cast ironmatrix and which is often desirable. Higher manganese also createsdifficulty in securing readily a homogeneous product during themanufacture of this addition alloy. Too much iron will have a similareffect during manufacture. Where the alloy does not contain anymanganese, the iron can be up to but should not exceed about 40%. If thealloy contains manganese, the sum of the iron and manganese should notexceed about 40%. If the alloy does not contain iron, the manganese canbe up to but should not exceed about 12%. Customary impurities such assulphur and phosphorus, and minor elements such as carbon, chromium,vanadium, titanium and molybdenum, can be present in an amount notexceeding a total of about 4%. Nickel is not included among these minorelements; it is present today in some pig irons and in most iron andsteel scrap and hence may be present in these alloys up to about 2% andis not detrimental to the functioning of the alloys. In my alloys,aluminum is a detrimental element if the amount exceeds about 1.5%, butit is preferably kept below 0.6%.

As previously stated, the alloys of this invention are uniform andhomogeneous in composition, rather than being a mere mechanical mixturesuch as may be obtained by pressing the ingredients into briquettes, oras contrasted with compositions in which only some but not all of theingredients are actually alloyed. It is a relatively simple matter toalloy magnesium and lead but such alloys, not containing silicon, arenot adequate for the purposes of this invention, as will be pointed outhereinafter. It is more difficult to produce a uniform, homogeneousalloy of lead, magnesium and silicon, but such alloys can be made bytaking suitable precautions, particularly by using relatively highmelting temperatures, as for instance temperatures above about 1900 F.,and in some instances temperatures approximating the minimum valuescustomarily employed in the casting of gray iron. The following areexamples of procedures by which uniform, homogeneous alloys according tomy invention can be made.

EXAMPLE A.Mg-Si-Pb ALLOY Charge: Grams Magnesium metal 4,000 97% siliconmetal (MW-H0 M.) 3,400 Lead 12,600

Total 20,000

All the magnesium metal was charged at the bottom of a plumbagocrucible, the 97% Si metal A+10 M.) was placed over the Mg metal, andfinally covered with part of the lead. The charge was melted down in agas furnace, the balance of the lead was added, the melt was heated toabout 1900 F., the alloy stirred well and poured into a cast iron ingotmold. The alloy analyzed:

Alloy N0. Mg Si Pb A 23. 28 15. 35 Balance.

EXAMPLE B.Mg-Si-Pb-Fe ALLOY Charge: Grams Lead-magnesium alloy (60 Pb-40Mg) 1,000 97% silicon metal (MW-+10 M.) 610 Lead 200 Steel punchingsTotal 2,000

The silicon metal, lead and steel punchings were melted down in a highfrequency furnace using a magnesia crucible. When the bath was molten,the lead-magnesium alloy was added, the bath was stirred well, and themolten alloy poured at about 2400 F. into a cast iron ingot mold. Thesolid alloy analyzed:

punchings and lead. This charge was melted in a high frequency furnaceand then heated to about 2200 F., the molten bath was stirred well, andpoured into a cast iron ingot mold. A very uniform, homogeneous ingotwas obtained. The final alloy analyzed:

Alloy No. Mg Si Pb Fe O c. 18. 13 28. 72 40. 06 Balance.

EXAMPLE D.Mg-Si-Pb-Mn ALLOY Charge; Grams Silicon-magnesium alloy (60Si-40 Mg) 627 Lead-magnesium alloy (60 Pb-40 Mg) 250 Lead 800Manganese-silicon alloy (62 Mn-21 Si) 323 Total 2,000

The above charge was melted down in a high frequency furnace using amagnesia crucible. The molten alloy was stirred well, and tapped atabout 2000 F. into a cast iron 1ngot mold. The alloy analyzed:

Alloy No. Mg Pb EXAMPLE E.-Mg-Si-Pb-Mn ALLOY Charge: Grams Magnesiummetal 400 97% silicon metal 10 M.) 400 Manganese metal (10 M.) 200 ead1,000

Total 2,000

Pb I Mn Each of these alloys A to E is a uniform, homogeneous alloy asshown by examination of its fracture. Each of the fractures was uniformand showed only a single constituent, there being no indication in thefracture of any of the original charge constituents.

My uniform, homogeneous alloys are a distinct improvement overcompositions known prior to my invention, and particularly in comparisonwith those compositions disclosed in Becket Patent 1,622,078. I havemade compositions corresponding to Examples I, II and III of the Becketpatent, and have used them in the treatment of molten cast iron and havefound that they are not nearly as effective as my uniform, homogeneousalloys, and have also found that they are distinctly less desirable forother reasons hereinafter referred to.

The following Example F corresponds to Example I of the Becket patent.

EXAMPLE F An alloy containing:

Per cent Lead 92 Magnesium 8 was made by melting down 11,000 grams oflead in a plumbago crucible heated in a gas furnace to a temperature ofabout 1000 F., and thereafter adding metallic magnesium in amountsufiicient to produce the alloy containing 92% lead and 8% magnesium.The magnesium dissolved readily in the bath. The molten bath was wellstirred, and then poured into a cast iron mold. The product of thisexample is hereinafter referred to as composition F. The fracture ofthis binary alloy showed a uniform, homogeneous product. Upon breakingthe alloy, the fracture became masked with a black, powdery productafter /2 to 1 minute exposure in air. When the alloy was crushed to 1"by down, the crushed product ignited spontaneously in air after about 3to 5 minutes, glowed intensely, and burned to a yellow powder. Theproduct, due to its instability, was entirely unsuited as an additionalloy.

The following Example G corresponds to Example II of the Becket patent,and the composition resulting therefrom is referred to hereinafter ascomposition G.

EXAMPLE G parts by weight of magnesium shavings were mixed with 56 partsby weight of lead shot and 34 parts by weight of a manganesersiliconalloy containing about 45% silicon and 55% manganese, and the mixturewas pressed into briquettes.

As is obvious from the method of making the briquettes and also as wasshown by examination of their fracture, the briquettes were merelyheterogeneous mechanical mixtures of the individual components of theoriginal mix.

The following Example H corresponds to Example III of the Becket:patent, the composition resulting therefrom being designated ascomposition H.

6 EXAMPLE H A mixture consisting of:

Grams Magnesium metal 2,550 Lead 8,400

was melted in a plumbago crucible heated in a gas furnace. This chargewas heated to 1600 F., stirred well, and then 2,025 grams of amanganese-silicon alloy (minus mesh) containing about 43% Si, 53% Mn and2%Fe was stirred into the molten bath and finally tapped into a castiron mold. Even after long soaking in the furnace, the finely crushedmanganese-silicon alloy was not dissolved in the molten magnesium-leadbath. The fracture of this cast showed a non-homogeneous com position inwhich the fine particles of the manganese-silicon alloy were entrappedin the magnesium-lead alloy. Furthermore, the cast product afterstanding in air for 24 hours disintegrated into a fine powder.

Tests were made to show the effectiveness of alloys B and C (accordingto the present invention) and compositions F, G and H (according to theBecket patent) when added to molten cast iron baths. The cast iron hadthe composition:

T. C. Si P The different addition agents containing magnesium were addedto the molten cast iron having a temperature of about 2700 F., the bathwas held /2 to 2 minutes, inoculated with 78% ferrosilicon, held to 1minute, and then cast into standard arbitration test bars (1.2" dia. x18" span). In heat No. 1, since composition F contained no silicon,0.27% silicon was added to the melt down charge to bring the finalsilicon content of the iron to the same level as the other heats. Thefive sets of bars were then subjected to bend tests. The results ofthese tests as well as other pertinent data are given in the followingtable:

Table Percent Si Cast Iron Mg Added by Breakmg Deflection, Heat Noposmon f Fe-Si f Inch Added Percent Inoculation bs.

F 0 55 0. 38 2, 127 0. 27 G 0 55 0. 38 1, 770 0. 24 H 0 55 0. 38 2, 0000. 25 B 0 45 0. 38 3, 495 0. 33 C 0 78 0. 38 3, 270 0. 28

The table shows that cast iron, treated with the uniform, homogeneousalloys (alloys B and C) of the present invention were greatly superiorto those produced either by alloy F made according to the Becket patentand containing 92% lead and 8% magnesium but no silicon, or by theheterogeneous briquette G made according to the Becket patent, or by thenon-homogeneous composition H made according to the Becket patent.

The amount of my uniform, homogeneous alloy to be added to molten castiron to be cast into gray iron castings, varies with the nature of theiron (as influenced by the raw materials used and the conditions ofprocessing during melting), the maximum temperature attained by themolten iron, the temperature at which the addition is made, the sulphurcontent of the iron, and perhaps other factors. In general, the additionapproximates 0.12 to 0.20% of contained magnesium, plus an amount ofcontained magnesium equal to 1 /2 times the sulphur content of the iron.This is not an absolute amount but varies acording of the precisecomposition of the alloy being used, as well as the various factorsinfluencing the character of the molten cast iron, as pointed out above,and the method of adding the alloy to the molten iron. It is, however, agood starting point in establishing the practice in a specific foundrywhile on a particular melting practice so that a limited amount ofexperimentation varying the addition upward and downward readilyestablishes the optimum addition required. In general, the amount ofalloy added should be such as to leave in the solidified cast iron atotal magnesium content of 0.04 to 0.10%, preferably 0.05 to 0.08%.

Another advantage possessed by these alloy addition agents is that ofincreased recovery of magnesium during both the manufacturing processand during use in the treatment of gray iron. Alloys Within these rangesof composition have the peculiar characteristic of being dissolvedsufficiently easily in cast iron that they may be effectively used atthe lowest customary pouring temperatures which characterize moderncommercial foundry practice. On the other hand, solution is sufficientlyslow that the alloy and its components will be uniformly distributedthroughout the melt and the magnesium will not be lost so rapidly as toprevent it from exerting its influence throughout the entire mass ofcast iron. Other than taking suitable precautions to protect againstlead fumes which may be released during treatment of the cast iron, noadditional care and no modifications of prior practice are required, theaddition of the alloy to iron that would otherwise cast gray, and of lowto moderate strength, being the sole requisite. The reason or reasonswhy these alloys melt at such critical rates so as to be usable at fulleffectiveness over such a wide range of casting temperatures, but stillmelt slowly enough so that all ingredients, and particularly themagnesium, are distributed uniformly throughout the cast iron, have notbeen clarified, but the observations have been sufficiently numerous tobe conclusive.

In improving the mechanical properties of the cast iron the alloyscovered by this invention regulate the microstructure of the gray ironso as to produce nodular graphite in substantial amount, usually to theextent of complete conversion of the carbon to this form.

Methods of sampling and analysis currently in use show after theaddition of the alloys of this invention that the carbon content and thesulphur content of the untreated irons have been reduced by thetreatment. The reduction in the sulhpur content is no doubt due to thecombination of magnesium with at least part of the sulphur and itsremoval as a slag or a slag forming constituent. The reason for thechange in the carbon content is not so obvious and it may be that thechange is apparent rather than real due to the difference in the formand the distribution of the carbon and creating a necessity fordifferent methods of sampling and analysis than those commonly in use.Completely satisfactory procedures have not yet been devised ordiscovered.

It has hitherto been an absolute requirement in the production of castiron having all or nearly all of its carbon in the form of spheroidsthat there be added following the addition of the magnesium alloy asecond addition rich in silicon, such. as ferrosilicon, the amount inmost cases being substantial. In the use of the alloys of thisinvention, such final addition of ferrosilicon is not a necessity andmay be dispensed with in many cases. of silicon represented by theaddition of the alloys according to my invention is very much less thanthat which would be added according to prior art methods subsequent tothe incorporation of the magnesium alloy. Even in those instances wherea final addition of silicon-rich alloy is made, the total siliconcontent represented by this addition plus the silicon content added bymeans of the magnesium-silicon-lead alloy is distinctly less than thesilicon added as a late ferrosilicon addition according to prior artmethods. When the late ferrosilicon addition is actually The amountemployed in conjunction with the alloys of this invention, the maximumamount of ferrite in the microstructure may be attained with a minimumsilicon addition, that is, attainable with the final chemicalcomposition of the iron, and through this means advantage in respect ofmachinability and reduction in the wear on tools used for machining willresult. Production of an iron with minimum pearlite for the chemicalcomposition also results in maximum ductility of the iron composition.

Alloys of this invention have also been added to molten steel forlowering the sulphur content of the steel. For example, steels have hadtheir sulphur content decreased flfiJlTl about 0.030% to about 0.020% bythe use of these a oys.

The invention is not limited to the preferred embodiment, but may beotherwise embodied or practiced within the scope of the followingclaims.

I claim:

1. A uniform, homogeneous alloy for addition to iron or steel, saidalloy consisting essentially of magnesium, silicon and lead except forcustomary impurities and minor elements in an amount not exceeding atotal of about 4% and except for nickel in an amount up to about 2%, thealloy containing about 5 to 30% magnesium, about to 40% silicon, andabout to 70% lead, said alloy resulting from solidification of acompletely liquid solution and upon fracture showing only a singleconstituent.

2. A uniform, homogeneous alloy for addition to iron or steel, saidalloy consisting essentially of magnesium, silicon, lead and iron exceptfor customary impurities and minor elements in an amount not exceeding atotal of about 4% and except for nickel in an amount up to about 2%, thealloy containing about 5 to magnesium, about 15 to silicon, about 20 tolead, and not over about 40% iron, said alloy resulting fromsolidification of a completely liquid solution and upon fracture showingonly a single constituent.

3. A uniform, homogeneous alloy for addition to iron or steel, saidalloy consisting essentially of magnesium, silicon, lead and manganeseexcept for customary impurities and minor elements in an amount notexceeding a total of about 4% and except for nickel in an amount up toabout 2%, the alloy containing about 5 to 30% magnesium, about 15 to 40%silicon, about 20 to 70% lead, and not over about 12% manganese, saidalloy resulting from solidification of a completely liquid solution andupon fracture showing only a single constituent.

4. A uniform, homogeneous alloy for addition to iron or steel, saidalloy consisting essentially of magnesium,

silicon, lead, iron and manganese except for customary impurities andminor elements in an amount not exceeding a total of about 4% and exceptfor nickel in an amount up to about 2%, the alloy containing about 5 to30% magnesium, about 15 to 40% silicon, about 20 to 70% lead, and notover about 12% manganese, the sum of the iron and manganese notexceeding about 40%, said alloy resulting from solidification of acompletely liquid solution and upon fracture showing only a singleconstituent.

References Cited in the file of this patent UNITED STATES PATENTS1,622,078 Becket Mar. 22, 1927 2,485,760 Millis et al. M Oct. 25, 1949

3. A UNIFORM HOMOGENEOUS ALLOY FOR ADDITION TO IRON OR STEEL, SAID ALLOYCONSISTING ESSENTIALLY OF MAGNESIUM, SILICON, LEAD AND MANGANESES EXCEPTFOR CUSTOMARY IMPURITIES AND MINOR ELEMENTS IN AN AMOUNT NOT EXCEEDING ATOTAL OF ABOUT 4% AND EXCEPT FOR NICKLE IN AN AMOUNT UP TO ABOUT 2%, THEALLOY CONTAINING ABOUT 5 TO 30% MAGNESIUM, ABOUT 15 TO 40% SILICON,ABOUT 20 TO 70% LEAD, AND NOT OVER ABOUT 12% MANGANESE, SAID ALLOYRESULTING FROM SOLIDIFICATION OF A COMPLETELY LIQUID SOLUTION AND UPONFRACTURE SHOWING ONLY A SINGLE CONSITUENT.